55.8-48.6 M.Y.A.
56 M.Y. A.
77°F (9° increase)
68°F
PALEOCENE EOCENE THERMAL MAXIMUM
EARLY EOCENE
The climate returned to Paleocene conditions.
But the new PETM mammals eventually dis-
placed Ectocion and its kind. Their descendants---
most hoofed animals alive today and every
monkey, ape, and human---transformed Earth.
As warming dried the Bighorn, bean-family
trees and lizards arrived from the south; dawn
redwoods shifted north. Modern primates and
hoofed mammals may have come from Asia,
crossing a forested Arctic land bridge.
Diacodexis was an early
artiodactyl; Hyracothe-
rium, a perissodactyl,
was the rst horse.
Cantius, a small primate,
had two modern fea-
tures: front-facing eyes
and grasping hands.
Now long extinct,
Prolimnocyon and
Meniscotherium were
new in the PETM.
Racoonlike Chriacus,
a Paleocene holdover,
preys here on a new
arrival from the south.
SEAN MCNAUGHTON
AND LAWSON PARKER,
NGM STAFF
ART: ALDO CHIAPPE
CONSULTANTS: SCOTT WING, SMITHSONIAN NATIONAL MUSEUM OF
NATURAL HISTORY; PHILIP GINGERICH, UNIVERSITY OF MICHIGAN;
WILLIAM CLYDE, UNIVERSITY OF NEW HAMPSHIRE; PATRICIA HOLROYD,
UC BERKELEY; KRISTER SMITH, SENCKENBERG MUSEUM
Not a mass extinction but a massive stirring of life: The PETM, as revealed by the fossils in
Wyoming s Bighorn Basin, is "a narrow interval when the world goes quite crazy," says paleo-
botanist Scott Wing. As plants and animals migrated poleward in the heat, the rst modern
primates and hoofed mammals---perissodactyls and artiodactyls---spread around the planet.
DAWN
REDWOOD
HACKBERRY
WATER FERN
ECTOCION
MENISCOTHERIUM
PROLIMNOCYON
GAULTIA
HYRACOTHERIUM
DIACODEXIS
PALMS
PALMS
SUZANNIWANA
COPAIFERA
BEAN FAMILY
CHRIACUS
CANTIUS
CANTIUS